code: def _equal_var_ttest_denom(v1, n1, v2, n2):
      df = n1 + n2 - 2.0
      svar = ((n1 - 1) * v1 + (n2 - 1) * v2) / df
      denom = mt_sqrt(svar * (1.0 / n1 + 1.0 / n2))  # XXX: np -> da
      return df, denom
  
file_path: mars/mars/tensor/stats/ttest.py
imports: from collections import namedtuple
  import numpy
  from scipy import __version__
  from scipy.stats import ttest_ind, ttest_ind_from_stats, ttest_rel, ttest_1samp
  from scipy.stats import distributions
  from ...core import ExecutableTuple
  from ...lib.version import parse
  from ..arithmetic import divide, sqrt, absolute, isnan
  from ..base import where
  from ..reduction import var, mean
  from ..utils import implement_scipy
label_desc: Use image node_id 1 for calling a global function with example usage: _equal_var_ttest_denom(v1, n1, v2, n2) and returns: df,  denom